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EVOLUTION Caution : these notes may change from the original... They are still evolving. SO WHAT IS EVOLUTION ANYWAY? Definition: A change over time More specifically: change in relative frequency of alleles in a population Note the word ―POPULATION” INDIVIDUALS DO NOT EVOLVE SOURCES OF CHANGE Sexual Reproduction ( Random Shuffling of alleles) Mutations Geographic isolation So, What does Darwin have to do with it? CHARLES DARWIN Born in England February 12, 1809 to a wealthy family attended Oxford University became a naturalist joined the crew of the H.M.S. Beagle for a 5 year voyage (1831) WHAT DARWIN LEARNED FROM THE VOYAGE made numerous observations and collected data that led him to propose a revolutionary hypothesis about the way life changes (evolution). DARWIN’S OBSERVATIONS: 1. Patterns of Diversity plants and animals are well suited to whatever environment they inhabit Different species live all over the world. Ex. Argentina, Australia, and England have similar grassland ecosystems, yet the animals inhabiting the areas were different. 2. Living Organisms and Fossils collected remains of preserved organisms called fossils. Some of the fossils resembled organisms that were still alive and others looked completely unlike any creature he had ever seen. 3. The Galapagos Islands characteristics of many animals and plants varied noticeably among the different Galapagos Islands. Ex. The tortoises shape of the shell corresponded to different habitats. ( Do not write) Hood Island tortoise – long neck and curved shell that is open and allows it reach sparse vegetation HOOD ISLAND ( RIGHT) Isabela Island(below) Pinta Island right OTHER ORGANISMS noticed that the finches on the Islands all had different beaks likely that a few finches founded the population but mutations over time allowed them to eat different foods. New beaks continued to be passed to the next generation which eventually led to different species VARIETY OF FINCHES Plants also undergo the same pressures of the environment Variety of vegetation found based on the type of climate that exists NATURAL SELECTION Definition: process by which individuals that are better suited to their environment survive and reproduce most successfully. THE PEPPERED MOTH Not a random process. — The mutation is random, but selection acts on that variation in a very non-random way: genetic variants that aid survival and reproduction are much more likely to become common than variants that don't. Natural selection is not random! (University of Berkeley) ARTIFICIAL SELECTION using genetic variation to improve crops or livestock ; artificial selection Artificial selection: nature provided the variation and humans select those variations that they found useful. 5 MAJOR POINTS TO THE NATURAL SELECTION HYPOTHESIS 1. Genetic variations exist in populations. Some variations are more favorable than others. These variations are inherited. 2. Organisms produce more offspring than can survive. Those that do not survive, do not reproduce. 3. Overproduction of offspring forces competition for resources. Darwin called this the struggle for existence. Not all offspring can possibly survive. 4. Individuals with favorable variations have more ―fitness‖ ;more likely to survive and pass those variations on to their offspring. 5. Species alive today are descended with modification from ancestral species that lived in the distant past. Darwin called this descent with modification. SURVIVAL OF THE FITTEST Link to Natural Selection example cartoon Adaptations: any inherited trait that increases the chances of survival and reproduction of an organism. Camouflage and Mimicry – allow animals with successful variations survive and reproduce EXAMPLES IN NATURE: Mimicry:Monarch and Viceroy, Moth and Bumblebee Camouflage: Squirrels, Leopards, walking sticks, Praying Mantis WHERE’S THE PROOF? Plentiful evidence: 1 Fossils 2 Geographical distribution 3 Homology 4. Vestigial Structures 5 Embryology 6 Biochemistry * (the chemistry of living organisms) FOSSILS 1) Fossils: Remnants of numerous organisms left behind Scientists can compare the bones of horses from 4 million years ago to ones from the present day. Fossils found in every layer of rock do not look the same as those from modern life. The oldest fossils are more different from the modern day organisms than the shallowest fossils Put pictures of fossils here! 2) GEOGRAPHIC DISTRIBUTION All over the world, there are similar animals in very far away places. Animals use different adaptations to survive in similar environments even though the environments are separated. Analogous Structures: Different in Structure but the same in function These do not show evidence of evolutionary relationships but, they do show natural selection 3. HOMOLOGY Many organisms have similar bones though not closely related. These are called Homologous structures. Suggest a common ancestor, shows strong evolutionary relationships Example: Birds, turtles, alligators, rats, humans, and whales all have ―finger bones‖ Put picture of human, horse, cat, bat, bird, whale here 4. VESTIGIAL STRUCTURES any structure that is so reduced in function or size that they are just vestiges or traces of the original structure. The structure may have been used in an ancestor. The structure may be used in another animal alive today. Examples: Appendix, small leg bones in pythons, pelvic bones in whales PICTURE OF VESTIGIAL STRUCTURES 4. EMBRYOLOGY Of animals with backbones, the embryonic stages look strikingly similar ; similar genes at work WHAT DOES THIS SUGGEST? Similar genes early in development Suggests a common ancestor and evolutionary relationships Groups of embryonic cells develop in the same order and in similar patterns The same set of genes control this development 5. BIOCHEMISTRY The more closely related organisms are, the more they will share in common biochemistry (the chemistry of what makes up their bodies) They share similar DNA sequences and proteins Relatively new means of identifying evolutionary relationships and has led to the reorganization of the history of several species. Chapter 16 notes CH. 16 IS ALL EVOLUTION THE SAME? • • • No, it does not happen in the same way across all populations. Natural selection on a single gene can just change the allelic frequencies With polygenic traits, it is more complicated. EVOLUTION CAN OCCUR IN THREE WAYS Directional selection Stabilizing Selection Disruptive Selection POPULATIONS If you think about the subtle varieties in a population, you get a bell-shaped curve The most common variety is represented in the middle and more extreme variations are on either end of the curve. * (hair color) Evolution shifts the curve by changing the percentage of each variation. DIRECTIONAL SELECTION In this case, Individuals on one end of the curve are better adapted to their environment. EXAMPLE: Beak size (finches) The birds with the medium beak are the majority. Small and large beaks are on the ends of the curve. If a drought occurs and only the very large seeds survive, only large-beaked birds will be able to eat. DIRECTIONAL SELECTION STABILIZING SELECTION When the average individual is best, the population stabilizes-reduces the percentage of organisms on the extremes Example: Birth weight in humans stays stable because too small a weight is harmful for the baby and too big a weight results in complications at birth. STABILIZING SELECTION DISRUPTIVE SELECTION This occurs when either extreme is better adapted for survival than the average. EXAMPLE: most of a species of a butterfly are brown. But, on either end of the population curve, you see RED and BLUE Brightly colored butterflies resemble very poisonous butterflies and thus, do not get eaten DISRUPTIVE SELECTION SMALL POPULATIONS The percentages of alleles change more quickly- GENETIC DRIFT If populations get separated and each new population only has two of the four variations, you have what is called a FOUNDER EFFECT GENETIC drift and FOUNDER EFFECT ARE POPULATIONS ALWAYS EVOLVING? No! Populations will remain stable if the following conditions are met: 1) Random mating 2) Large population 3) No movement into or out of population 4) No mutations 5) No natural Selection THIS IS KNOWN AS THE HARDY- WEINBURG PRINCIPLE It is difficult for all of the conditions to be met. dIt There, SO, HOW DO WE GET A NEW SPECIES All of these changes over time can eventually lead to a new species A species is defined as a group of organisms that can interbreed and produce fertile offspring This process is called SPECIATION Caused by 3 isolating mechanisms: Behavioral, Geographic, and temporal BEHAVIORAL ISOLATION Occurs when two populations are capable of interbreeding but do not. (due to difference in rituals/ behaviors) EX: Eastern and Western meadowlarks both live in central US They do not mate because they use different songs to attract their mates GEOGRAPHIC ISOLATION Geographic isolation occurs when 2 populations cannot reach each other to mate due to a physical barrier. EX: earthquake in CA creates a huge crevasse in the ground, isolating a population of lizards Since the two populations cannot mate, they begin to have subtle changes over time that make them different species OTHER ANIMALS THAT OBEY GEOGRAPHIC ISOLATION Picture of mice? TEMPORAL ISOLATION Occurs when the species reproduce at different times of the year. EX: 3 species of orchid all live in the same area but, they never interbreed because they release their pollen at different times of the year. Put picture of orchids and/ or other animals that obey temporal speciation PATTERNS OF EVOLUTION IN POPULATIONS Adaptive radiation Convergent evolution Coevolution extinction ADAPTIVE RADIATION A single species evolves into more populations by creating adaptations to different environments or niches EX: Darwin’s finches – beak mutations led to access of different food supplies CONVERGENT EVOLUTION Unrelated organisms resemble each other since they have adapted to the same environment. Ex: fish and dolphins both have fins Birds and dragonflies both have wings These are called analogous structures ( same function but different structure) COEVOLUTION When two species evolve in response to one another EX: Flowers and their pollinators must evolve together. If the flower has a mutation that no longer attracts the hummingbird, it will not reproduce….and then, the hummingbird will have to find a new food source. EXTINCTION When a species cannot adapt to its changing environment Competition Climate change HOW FAST CAN EVOLUTION OCCUR? Gradualism- when evolution occurs slowly over time ( most of what we have talked about) Punctuated Equilibrium – when a major event changes the distribution of a population…leads to a quick burst of changes since mutations spread quickly through small populations CH. 16. A BRIEF HISTORY OF TIME By looking at the fossil record, scientists have learned that not all types of animals appeared all at once. Using one of a variety of techniques, they can figure out which ones are older. 1) Relative: compare to others found in the same layer 2) Radioactive: uses isotopes and their predictable rate of decay A BRIEF HISTORY OF TIME Earth’s atmosphere did not contain oxygen, so microorganisms were the first to appear (prokaryotic) ….in the water Once oxygen appears, eukaryotic organisms appear Theory of Endosymbiosis – Eukaryotes arose from prokaryotes that lived as a community THEORY OF ENDOSYMBIOSIS Ex. A prokaryote that does photosynthesis lives inside another simple cell. Eventually their DNA merges together ( one genome instead of 2) A new, more complicated organism results TIMELINE 1 Fish / simple plants 2 Amphibians 3 Reptiles and bush-like plants 4 Birds / trees 5 Simple Mammals 6 Finally Primates A BRIEF HISTORY OF TIME Since all organisms have appeared sequentially, it would seem logical to assume that each gave rise to the other….. This is not quite the case. Evolution argues that organisms share ancestors not that one evolved into another. TURNING INTO A TETRAPOD ( 4 LEGS) So much to learn, so little time! Evolution is a whole course in college all by itself!